The P50 predicts conscious perception under tactile but not electrical somatosensory stimulation in human EEG

Past research has not reached consensus about the neural correlates of conscious somatosensory perception. Different studies have identified ERP components at various latencies as predictors of somatosensory detection, but it is still largely unclear which factors are responsible for this variation. Here, for the first time we directly compare the event-related potential correlates of stimulus detection under tactile versus electrical peri-threshold stimulation in a between-groups design, while controlling for task-relevance and post-perceptual processes with a visual-somatosensory matching task. We show that the P50 component predicts conscious perception under tactile, but not electrical stimulation: while electrical stimulation evokes a P50 already for subliminal stimuli, there is no subliminal P50 for tactile stimulation. In contrast, the P100 and N140 components robustly predict conscious detection in both stimulation groups. Tactile stimulation produced a clearly separable N80 component for detected stimuli, that appeared as part of the N140 under electrical stimulation. The P300 predicted conscious detection even though we controlled for post-perceptual processes, suggesting that it partly reflects aspects of subjective experience. Our results demonstrate that the neural correlates of somatosensory detection depend on the type of stimulation used, limiting the scope of previous results achieved using electrical stimulation.